Aromatic polyamide and/or aromatic polyimide film and magnetic recording medium having such a film as a base

Abstract

An aromatic polyamide and/or aromatic polyimide film suitable as a support in a magnetic recording medium excellent in runnability and scratch resistance and good in S/N ratio comprises an aromatic polyamide and/or aromatic polyimide as a main component, with particles present in the film, which film has characteristics which satisfy the following formulae: 10 nm≦dmax≦300 nm (1) 3≦ρ(dmax)/ρ(dmin)≦100 (2) or 10 nm≦dmax≦300 nm (3) 3≦ρ(dmax)/ρ(d")≦100 (4) ρ(dmax)/ρ(dmin)>100 (5) where dmax is the depth from a first surface of the film at which the particle density shows the first maximal value; dmin is the depth at which the particle density shows the first minimal or minimum value in a range from dmax to 1 μm from the said first surface; the linear differential coefficient of the particle density distribution curve has an inflection point at which the quadratic differential coefficient of the particle density distribution curve ia a negative, which inflection point occurs at a depth d", deeper than dmax, and within a range between the depth at which ρ(d) is 4/5 of ρ(dmax), and dmin; and ρ(d) is the particle density at each depth.

We claim: 
     
       1. A polymeric film comprising a main component selected from the group consisting of an aromatic polyamide, an aromatic polyimide, and their mixtures, said film containing particles, having particle distribution characteristics, at least one surface portion of said film having particle distribution characteristics satisfying both of the following formulae:   10 nm≦dmax≦300 nm                            (1)       3≦ρ(dmax)/ρ(dmin)≦100                (2)     where dmax is the depth from said surface of said film at which the particle density has a maximal value; dmin is the depth from the said surface of said film at which the particle density has a minimal or a minimum value in a range from dmax to 1 μm from said surface; and wherein ρ(d) is the particle density at each depth.   
     
     
       2. A film, which comprises a main component selected from the group consisting of an aromatic polyamide, an aromatic polyimide, and their mixtures, said film containing particles, having particle distribution characteristics measured from a surface portion of said film, said particle distribution characteristics satisfying the following formulae:   10 nm≦dmax<300 nm                                   (3)       3≦ρ(dmax)/ρ(d")≦100                  (4)       ρ(dmax)/ρ(dmin)>100                                (5)     where dmax is the depth from a first surface of said film at which the particle density possesses a first maximal value; wherein dmin is the depth from the said first surface at which the particle density possesses a first minimal or first minimum value in a range from dmax to 1 μm from the said first surface; and wherein the linear differential coefficient of said particle density distribution curve has an inflection point at which the quadratic differential coefficient of said particle density distribution curve is a negative, which inflection point occurs at a depth d" which is deeper than dmax, and within a range between the depth at which ρ(d) is 4/5 of ρ(dmax), and dmin; and wherein ρ(d) is the particle density at each depth.   
     
     
       3. The film according to claim 1 or 2, wherein the average particle size of said particles contained in said film is in a range from 5 nm to 500 nm, and wherein the relative standard deviation of the particle size distribution of said particles is 0.7 or less. 
     
     
       4. The film according to claim 1 or 2, wherein at a depth Dmax from a second surface of the film opposite the first surface the particle density possesses a first maximal value of said particle density (if Dmax also satisfies the formulae (1) and (2) or the formulae (3) to (5), it is defined as ρ(dmax)≧ρ(Dmax), the following formula is satisfied:   ρ(dmax)/ρ(Dmax)≧1.2                         (6).     
     
     
       5. The film according to claim 1 or 2, wherein the average height h of surface protrusions formed on said first surface of the film, the relative standard deviation σ/h of the distribution of protrusion heights, and the ratio P 1/3   of the number of protrusions with heights of 1/3 or less of the average protrusion height h to the total number of protrusions satisfy the following formulae:   5 nm≦h≦100 nm                                (7)       σ/h≦0.7                                       (8)       P.sub.1/3 ≦20%                                      (9).     6.   
     
     
       6. The film according to claim 1 or 2, wherein there is a minimal value of particle density in a thickness range from dmax to 1 μm from the said first surface of the film. 
     
     
       7. The film according to claim 1 or 2, wherein the thickness of said film is about 6.5 μm or less. 
     
     
       8. The film according to claim 1 or 2, wherein said film is a single layer film or a laminate film suitable as a base film for a magnetic recording medium. 
     
     
       9. A magnetic recording medium comprising a magnetic layer formed on at least the said first surface of an aromatic polyamide and/or aromatic polyimide film according to claim 1 or 2. 
     
     
       10. A magnetic recording medium comprising a magnetic layer formed on a second surface opposite to the said first surface of a film according to claim 1 or 2. 
     
     
       11. A magnetic recording medium according to claim 9, which is a magnetic tape of 2.3 to 13.0 nm in width, 6.5 μm or less in film thickness, 100 m/coil or more in length and 8 kilobytes/mm 2  or more in recording density as a magnetic recording medium. 
     
     
       12. A magnetic recording medium according to claim 10, which is a magnetic tape of 2.3 to 13.0 mm in width, 6.5 μm or less in film thickness, 100 m/coil or more in length and 8 kilobytes/mm 2  or more in recording density as a magnetic recording medium.